A Comparison of Randomizing Either One Eye or Both Eyes in Clinical Trials for Stargardt Disease Type 1

Designing a clinical trial for rare diseases such as Stargardt disease type 1 is challenging due to the limited patient population. In traditional clinical trial designs for inherited retinal diseases, often only 1 eye of each patient is used as the treated eye or the sham, disregarding half of the available eyes.This study explores a trial design in which both eyes are included, with the fellow eye serving as the control, maximizing the use of available data and enhancing statistical power.

Retrospective analysis of natural history data to conduct sample size calculations.

Patients with genetically solved Stargardt disease type 1 who had at least 2 fundus autofluorescence measurements obtained within 5 years of each other. Retrospective data of 164 patients were included for analysis.

The required sample sizes for 1-eye and paired-eye study designs were calculated using retrospective natural history data on the progression of definitely decreased autofluorescence quantified from fundus autofluorescence imaging.

Required sample size for a clinical trial.

Sample size calculations showed that 170 patients are needed for a 2-year clinical trial with a 1-eye design, decreasing to 99 patients for a 5-year trial. When using a paired-eye design, 64 patients are needed in a 2-year trial, decreasing to 28 patients in a 5-year trial. When using a paired-eye design and requiring definitely decreased autofluorescence atrophy in both eyes at inclusion, 37 patients were needed in a 2-year trial, decreasing to 16 patients in a 5-year trial.

Using a paired-eye design for a clinical trial in Stargardt disease type 1, with definitely decreased autofluorescence atrophy growth rate as the primary end point, is more efficient than a 1-eye design. Implementing additional inclusion criteria, such as requiring definitely decreased autofluorescence atrophy in both eyes at baseline, further reduces the number of patients needed to achieve sufficient statistical power. This approach enhances the feasibility for trials in Stargardt disease type 1 where patient availability is limited.

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